1. Field to the Invention
This invention relates to an erasing device for erasing a signal recorded on a magnetic recording medium.
2. Description of the Related Art
In the past, for example, the still video systems, when erasing the recorded information, have generally adopted the DC erasing method in which the direction of flow of direct current to the magnetic head is changed in each rotation of the magnetic disc and the level of the current gets progressively lower, or the AC erasing method in which alternating current flows to the magnetic head. In this AC erasing method, an erasing signal is made progressively lower so as not to leave the direct current magnetization on the disc, as is well known in the art. Here, the conventional method of lowering the level of the erasing signal is disclosed in Japanese Laid-Open patent application No. Sho 62-26911, in which an output of a trapezoidal wave generating circuit and an erasing reference signal pass an amplitude modulator to produce a progressively lowering erasing signal.
Another erasing device in which the erasing is carried out by supplying alternating current whose polarity inverts in each one rotation of the magnetic disc to the magnetic head is disclosed in Japanese Laid-Open patent application No. Sho 61-175905.
A circuit embodying the above-described conventional example is shown in FIG. 1.
The circuit of FIG. 1 is an output impedance converting circuit in which in response to a circuit actuating pulse output from an input terminal 42 an erasing reference signal is output from a terminal 41 to an output terminal 43, and attenuation starts at a time when the actuating pulse is changed to a low level. In this circuit, the impedance of the output stage must be sufficiently small compared with the impedance of that circuit which is connected ahead of the output terminal 43. If it is insufficient, the erasing reference signal would be supplied to the output terminal 43, thus causing the circuit to be in the erasing state. For this reason, it is necessary to leave a current flowing to the output stage during all the time when the system is in operation. However, concerning the apparatus using a dry battery in driving the system, for example, the electronic still camera, electrical energy is very wastefully used up when a current supply to the circuit which does not partake the operation of the system is maintained during that operation.
Also, in connection with a block diagram mentioned in Japanese Laid-Open patent application No. Sho 61-175905, which is shown in FIG. 2, it should be pointed out that in the case of using the method described in Japanese Laid-Open patent application No. Sho 61-175905, there is a drawback that when the read means 51 and the memory means 52 are imparted into the circuit, its scale of construction is greatly increased.